Synthesis of N-Fused Benzimidazole-4,7-diones via Sequential Copper-Catalyzed C-N Coupling/Cyclization and Oxidation.

2-(2-Bromovinyl)- and 2-(2-bromoaryl)-benzimidazoles, including their 4,7-dimethoxy analogs, react with primary amides by microwave irradiation (or usual heating) in dimethylformamide in the presence of a catalytic amount of CuI along with a base to give the corresponding benzo[4,5]imidazo[1,2-]-pyrimidines and -quinazolines in good yields. Treatment of benzo[4,5]imidazo[1,2-]-pyrimidines and -quinazolines having methoxy group on benzimidazole moiety with aqueous ceric ammonium nitrate affords unprecedented N-fused hybrid scaffolds, benzo[4,5]imidazo[1,2-]-pyrimidin-6,9-diones and -quinazoline-8,11-diones, respectively, in high yields.